A current method in the art used to manufacture flexible tubular bodies of steerable catheters or sheaths is to form the body on a mandrel using multiple layers: an inner liner intended to define the central lumen of the body; a layer of wire braid for reinforcing the body; and an outer thermoplastic jacket. The inner liner is pulled over the mandrel and tightened down. Deflection wires used to deflect the distal tip of the body are laid axially along the inner liner. The layer of wire braid is pulled or woven over the inner liner and deflection wires. After the wire braid is tightened down, the entire body is encased in a thermoplastic outer jacket. The outer jacket is then encased in heat-shrink material and heated. The heat causes the thermoplastic jacket layer to flow, which, when teamed with the pressure from the heat-shrink material, causes the thermoplastic outer jacket to impregnate the wire braid and embed the deflection wires. This consolidates the body into one integral unit.
Embedding the deflection wires in the flexible tubular body via the action of the thermoplastic polymer teamed with the heat-shrink material allows the deflection wires to create their own wire lumens. However, the deflection wires and the resulting wire lumens end up being approximately equal in diameter. This creates three related difficulties. First, significant deflection wire actuation friction is created between the walls of the wire lumens and the deflection wires as an operator attempts to deflect the body by moving the deflection wires. This actuation friction increases the difficulty in operating the deflection wires. Second, as the distal end of the body is deflected (bent) through the movement of the deflection wires, the wire braid embedded in the outer wall of the body is also flexed. As the wire braid flexes, the forces created can deform the central lumen. This can cause the wire braid to lock down on the deflection wires and the wire lumens. This greatly increases the deflection wire actuation friction and can prevent movement of the deflection wires as the wire lumens are deformed from a circular shape into an ovular shape. The third problem is that as the deflection wires are “locked down” in the bent body, the deflection wires and body loses the ability to spring back to the original shape as the force on the deflection wires from the operator at the proximal end is removed.
To overcome the aforementioned difficulties, U.S. Pat. No. 6,582,536 to Shimada, which issued Jun. 24, 2003, teaches creating flexible tubular bodies with lumens that are larger in diameter than the deflection wires to be received in the lumens. To achieve such an arrangement, a lumen defining wire is embedded in the outer thermoplastic jacket of the body to define a lumen. The lumen defining wire has a diameter that exceeds the diameter of the deflection wire to be received in the lumen. Once the oversized lumen is formed, the lumen defining wire is removed and the deflection wire is inserted into the oversized lumen.
The method taught in the Shimada patent helps reduce the deflection wire actuation friction and locking problems associated with deflection wires and their lumens. However, it does so at the cost of increased manufacturing complication, waste and, as a result, expense.
There is a need in the art for a less expensive method of manufacturing a flexible tubular body with deflection wires that generate less deflection wire actuation friction and are less likely to lock when the body is being deflected. There is also a need in the art for a flexible tubular body manufactured according to said method.